1. Field of the Invention
The present invention relates to an exposure apparatus, a device manufacturing method using the same, and a gas supply device.
2. Description of the Related Art
An exposure apparatus is an apparatus that transfers a pattern of an original (reticle or mask) onto a photosensitive substrate (e.g., wafer, glass plate, or the like, where the surface thereof is coated with a resist layer) via a projection optical system in a lithography process of a manufacturing process for a semiconductor device, a liquid crystal display device, or the like. The exposure apparatus generally includes a chamber that surrounds the entire exposure apparatus. The chamber circulates air to keep it clean while keeping the ambient temperature of the exposure apparatus body constant. The chamber mainly includes an air conditioning machine room that performs air temperature control, a dust collecting filter that filters micro foreign matter to thereby form a uniform flow of clean air, and a booth that isolates the apparatus environment from the outside. In this case, temperature-controlled air is supplied into the booth via the dust collecting filter and the like using an air blower provided inside the air conditioning machine room. The supplied air is again taken into the air conditioning machine room from the return port disposed at the booth to thereby circulate in the chamber. In order to prevent micro foreign matter or harmful gas from entering into the interior of the exposure apparatus through minute clearances of the booth, the chamber is controlled such that outside air, which corresponds to approximately 0.1 of the amount of circulation air, is introduced from an outside-air introduction port provided in the air conditioning machine room to thereby constantly maintain the air pressure in the booth at a positive pressure. However, when the exposure apparatus is operated over a long period of time, the circulation air in the booth comes into contact with the final optical members that configure an illumination optical system, and the projection lenses that respectively configures the top surface and the bottom surface of the projection optical system to thereby make the surfaces of these optical elements cloudy. Consequently, the productivity of the exposure apparatus undesirably decreases due to illumination deterioration of exposure light. Therefore, in a conventional exposure apparatus, the final optical members of the illumination optical system and the projection lenses of the projection optical system are purged by clean inert gas such as nitrogen gas or the like, whereby the occurrence of fogging on these optical elements is suppressed to low level.
In addition, the air in the clean room where the exposure apparatus is installed generally includes minute quantities of chemical pollutants such as basic gas (ammonia, amine, and the like), acidic gas (sulfuric acid, nitric acid, hydrogen chloride, and the like), and organic gas (siloxane, and the like). These gases are also discharged in minute quantities from the components of the exposure apparatus. Hence, a conventional chamber includes a chemical filter in order to reduce the concentration of the chemicals contained in the air within the booth below a ppb level. The chemical filter is a filter that removes basic gas and acidic gas using an ion exchange reaction or removes organic gas using an activated carbon. For example, the chemical filter having the side of 600 mm and the thickness of 60 mm is employed in a stacked configuration in accordance with the installation environment and the required reduction in the concentration. However, when the amount of circulation of air within the booth increases accompanying the increasing size of exposure apparatuses, a chemical filter with a larger opening, which reduces the face velocity in the plane of the chemical filter, needs to be selected in order to improve the adsorption efficiency. Furthermore, when the amount of air to be taken from the outside of the booth increases, the amount of basic gas, acidic gas, and organic gas to be taken from inside the clean room also increases, resulting in a reduction in lifetime of the chemical filter. Specifically, in order to extend the replacement cycle and reduce the down time of the exposure apparatus, more chemical filters need to be provided, resulting in the increased size of the exposure apparatus.
In contrast, in order to suppress fogging on the optical elements while avoiding increasing the size of the exposure apparatus, there is a method for locally purging each of the optical element portions in contact with air within the booth with humidified air. The flow rate of humidified air is a low flow rate from one per thousands to one per tens of thousands compared to that of circulation air. The method is an energy-saving system compared with the method for removing pollutants from all circulation air to thereby lower the concentration to a required level. As a method using humidified air, Japanese Patent Laid-Open No. 9-275054 discloses a semiconductor exposure apparatus that controls the humidification of clean dry air (hereinafter referred to as “CDA”) supplied from the production facility to thereby supply the clean dry air via a chemical filter into the apparatus. Examples of the humidifying method to be used in the semiconductor exposure apparatus include a method for adjusting the temperature of a humidifier using a humidity sensor, and a method for controlling the flow rate of CDA to be sent to the humidifier. The semiconductor exposure apparatus ejects humidified air onto the surfaces of the optical elements and lowers the concentration of chemical pollutants contained in the atmosphere near the surfaces thereof for fogging prevention. The aforementioned humidified air is a generic name for gas having a dew-point temperature of 0 degrees Celsius or above, in which most of impurities are removed to the same level as CDA, whereas CDA is very dried air having a dew-point temperature of about −60 degrees Celsius.
However, the semiconductor exposure apparatus disclosed in Japanese Patent Laid-Open No. 9-275054 adjusts the amount of humidification of CDA by changing the temperature of an object or liquid. In this case, the thermal time constant of an object or liquid is relatively high, and consequently a highly-accurate humidity control cannot be performed. On the other hand, unlike the method using heat, in the method for controlling the flow rate of CDA to be sent to the humidifier, the effect of the thermal time constant of an object or liquid is reduced, whereby a highly-accurate humidity control can be performed. However, it is essential that the performance of a humidifying medium be in a predetermined range, and thus, a change in the performance of a humidifying medium cannot be ignored. Here, the performance of a humidifying medium includes, for example, a saturated steam pressure that varies depending on the temperature of CDA. Furthermore, in a vaporizing humidification method, the heat is removed from the surroundings by means of heat of vaporization when liquid is vaporized. Consequently, the temperature of liquid is reduced, and thus the saturated steam pressure is also reduced, resulting in a reduction in the absolute humidity of gas passed through the humidifier. Furthermore, from the viewpoint of the fluctuation of a laser interferometer, it is desirable that humidity be controlled following the humidity inside the space. However, liquid to be supplied to the humidifier may be directly supplied from the place where the humidifier is installed, so that the temperature of liquid may not always be controlled. The same also applies because the temperature fluctuation under the environment where the humidifier is placed also depends on the place where the humidifier is installed.